It is updated by the government of india every five years.they add name of those who are eligable and delete the names of those who are dead.
It is updated by the Election commission before the elections take place.
They add the people who are now eligible to vote, i.e, aged 18 people.
and they remove the people who are not alive now. 
The election Commission does so, to know the total number of actual voters and after the election they declare the percentage of the people who participated in the election.

Thank you.....!!!!
Mark as brainliest of helpful..
Yours, Jahnavi.